(1) Field of the Invention
The present invention relates to an apparatus for detecting torque of an oscillation-type electric dynamometer.
(2) Background of the Art
Japanese Patent Application second (Examined) Publications No. sho 58-25217 published on May 26, 1983 and No. sho 62-26699 published on June 10, 1987 exemplify apparatus for detecting a quantity of torque for oscillation-type dynamometers.
Such dynamometers are used to test various kinds of performance of an equipment to be tested, such as an engine, by adjusting a brake force and/or driving force of an electric motor, etc., against a torque and/or inertia force generated by the equipment under test.
One of the dynamometers includes an oscillation-type dynamometer having a torque controlling system of an electric motor in which an oscillator, supported by means of a floating apparatus so as to enable free oscillation, receives a rotational force, the rotational force is converted into a strain generated on a load cell engaging a torque arm extended from the oscillator, and a torque detection signal amplified from the strain on the load cell serves as a feedback signal of the torque controlling system constituted by the electric motor.
In the above-described oscillation-type electric dynamometer, a responsive characteristic of the torque controlling system using the dynamometer has been reduced due to delays of strain detections in the load cell and associated strain amplifier to be described later and caused by an inertia of the oscillator and due to ripples, vibrations, and noises caused by natural vibrations of the load cell and anti-vibration rubber member in the torque detection signal.
These disadvantages are basically caused by vibrations generated due to the inertia of the oscillator. In the above-identified Japanese patent Application Second publications, the vibrations generated due to the inertia of the oscillator are detected and the detected vibrations are added to the detected torque quantities with a reverse polarity to an output signal derived from the load cell so that unnecessary signal components included in the output signal of the load cell are cancelled.
However, the torque detecting apparatus disclosed in the above-identified Japanese Patent Application Second Publications drawbacks as will be described below.
That is to say, the torque detecting apparatus described above includes a vibration detector, installed on the torque arm extended from the oscillator, for detecting the vibration of the torque arm in the direction in which the torque arm applies a force to the load cell. The detected signal is used to correct the output signal of the load cell. The torque detecting apparatus further includes a strain amplifier which transducers the output signal of the load cell into a corresponding torque detection voltage; another amplifier, connected to the vibration detector, for amplifying the detection signal of the vibration detector; a coefficient setting/adding circuit, connected to the other amplifier via a filter and low-level signal elimination circuit, for calculating a coefficient to be combined with the acceleration amplified vibration detection signal; and an adder for adding the coefficient combined vibration detection signal to the torque detection voltage derived from the strain amplifier and for outputting the added signal as a torque detection output.
Although the above-described torque detecting apparatus can make a remarkable improvement of measurement accuracy of the torque reduced due to variations of zero point, enhancing the responsive characteristic of the torque detection signal from the torque detecting apparatus, a signal level clipped by means of the low-level elimination circuit needs to be made large when a temperature change which affects the output signal of the vibration detector becomes large so that the zero point of the torque detection signal is deviated from a real zero point.
Therefore, all detection signals whose levels are smaller than a clip level set by means of the low-level signal component elimination circuit are eliminated. In addition, although it becomes effective to detect the torque in states where impact absorption occurs within a gap between a knife edge of the torque arm and load cell and where the knife edge is fitted into the load cell with the gap provided, a correct torque waveform of the detection output of the adder becomes distorted due to a clipped real vibration detection signal in a state where the torque is applied to the load cell whose level exceeds a certain magnitude.